The present invention describes the preparation of heptabromodibenzofuran and its use as a flameproofing agent. The subject matter of the invention is highly brominated dibenzofurans of the formula ##STR2## WHEREIN X + Y = 6.0 TO 7.0, PREFERABLY 6.5 TO 7.0, AND Y = 0 TO 0.3. Particularly advantageous are highly brominated dibenzofurans having a bromine content equal to or greater than 75% by weight and a chlorine content equal to or less than 2% by weight. Additional subject matter is the new substance, heptabromodibenzofuran.
Highly brominated diphenyl ethers, such as octa- or decabromodiphenyl ether, have long been used as good flameproofing agents, especially in conjunction with synergists such as antimony oxide.
With regard to the cyclic ethers, only the tri- and tetrabromination of 2,4,8-trichlorodibenzofuran is known (German "Offenlegungsschrift" No. 2,411,665 of Ciba-Geigy AG), but a perbrominated dibenzofuran is unknown.